You should watch the whole video. From memory, the video author claims that the books are not based directly on the recordings nor on material that Feynman wrote himself, but rather on lecture notes written by another professor who had to cover for Feynman (who is also listed as one of the authors in the book). She also mentions how those lecture notes from this other professor correct some small mistakes Feynman made in some calculations and diagrams from the lecture. Her claim is that Feynman was not the person who actually wrote the text of the book.